The invention relates to a steering device for motor vehicles with a steering shaft.
Steering devices for motor vehicles are frequently implemented in two parts, one slidable into the other. In the event of a frontal collision the steering device does not endanger the driver because the steering device yields upon impact of the body onto the steering wheel and the impact energy is absorbed. In known devices, the slidable steering shaft tube, which receives the control wheel-side steering shaft, is disposed in a casing which is clamped with respect to the motor vehicle chassis by machine screw fastening in a predetermined position. The machine screw fastening is herein implemented such that upon impact, the steering wheel side shaft end with an axially directed and machine screwed casing bracket, is movable along a specific path. The impact energy is correspondingly absorbed by the machine screwed clamping. In order to make the energy absorption more uniform in the event of impact, additional energy absorption elements are disposed between the longitudinally slidable shaft and the chassis of the motor vehicle. An energy absorption element, which is implemented as a sheet metal tongue that can be torn away, is for example known in the art from GB 1,390,889.
One disadvantage of known crash systems for steering columns is that the break-free force cannot be defined over wide ranges independent of the energy absorption force. Also, the absorption behavior cannot be reproducibly preset.
The object of the present invention is to propose a crash system for a steering column configuration, which eliminates the disadvantages of the prior art. In particular, the object is to provide a crash system for steering columns which permits break-free force and a defined energy absorption with reproducible behavior. In addition, the configuration must be simply mounted and produced economically.
According to the invention the configuration is implemented such that in the event of an impact the break-free force is separated from the energy absorption force upon sliding of the steering shaft.
Thus, in the event of a crash the clamped break-free element is released immediately to dissipate the impact energy. As a result, the energy absorption over the defined displacement path is no longer substantially affected by undefined clamping forces and the absorption effect is predetermined through the implementation of the absorption element.
In one embodiment, clamping forces exist between a casing bracket and a stationary chassis, and the facing portions pressed onto one another through the clamping are slightly inclined with respect to a sliding direction. As a result of being disposed at a specific wedge angle, a short displacement path already exists and the original clamping is immediately reduced because the two wedge face parts move apart according to the angular slope. In case of an impact the clamping is already broken after a displacement of a few tenths of a millimeter and the further displacement is no longer determined by undefined clamping forces. The casing bracket, which is fixed to the steering shaft tube, is also connected to the chassis via a tearaway strip. The implementation of this tear-away strip determines the degree and the time course of the energy absorption behavior. The energy absorption behavior can be optimized for a more gentle interaction with the driver by adjustment of the dimensions of the tear-away flap.
Another preferred embodiment includes elevations in the region of the compressed slide facing, that are disposed on both sides of the facing. The elevations keep each other immovable over a short distance. The slide facing is the contact zone of the elevations. In the case of displacement, i.e. in the event of a breaking-free, one elevation slides a short distance, such as for example of a few millimeters, from the other elevation and thus generates the desired breaking free in the event of a crash.
Another preferred embodiment includes a break-free element with at least one subregion of the clamped facing parts where the opposing clamping faces are stair-stepped such that the clamping force is reduced after a short displacement path.
An especially cost-effective and space-saving steering column configuration with a system for energy absorption comprises a steering shaft supported in a guide box which, is fixedly connected to a retaining bracket. The retaining bracket comprises laterally flange-like slide faces which are clamped tightly on the motor vehicle chassis via machine screws. The clamping is implemented in such a manner that in the event of a crash the steering shaft can be displaced by several centimeters with the bracket. The energy absorption element is connected stationarily to the chassis and to the point of energy absorption due to the displacement of the bracket with the steering shaft. The absorption element is preferably implemented as a sheet metal part with a tear-away flap, which developed, for example, in the form of a yoke as a tear frame, is mounted between the bracket flange and the chassis. This embodiment is advantageous because the attachment of the configuration to the chassis is possible using only two attachment means, preferably two machine screws. This simplifies the implementation considerably and also permits a rapid mounting which has a positive effect on the total cost. The tightening torque of the machine screws is advantageously in the range of 15 to 35 Nm. This simple implementation of the configuration and the feasibility of securing the entire configuration with only two attachment machine screws without separate bracket guidance, permits use of the invention without previously described special break-free elements. But in this case the separation between the break-free force and energy absorption is less unique. However, the configuration is cost-effective.
The invention will be explained in further detail in conjunction with embodiments and accompanying schematic figures.